Linux系统下搭建PX4/Pixhawk原生固件编译环境

对于新版本的固件V1.11.3,在pixhawk官网可以找到开发环境的搭建，这里把开发环境链接贴出来：https://docs.px4.io/master/zh/dev_setup/dev_env_linux_ubuntu.html
但是新版本的代码过于复杂，有时候想要学习代码可以下载老版本的代码，但是经过实验发现，搭建好的新版本的环境编译老版本的代码经常出错，因此将自己实验过程中出现的一些错误总结下来：
1.下载代码的时候，不要直接git clone 要指定版本信息，如下所示：

git clone -b v1.8.2 https://github.com.cnpmjs.org/PX4/PX4-Autopilot.git

这里我指定了版本信息是v1.8.2，同时可以发现我的网页并没有直接使用github，而是使用的国内的镜像.cnpmjs.org，这样下载起来代码会快10倍左右。
2. 下载好代码，大概两分钟左右，使用指令git submodule update --init --recursive更新子模块，但是这里的子模块也是使用的github上的资源，下载起来超级慢，两三天都有可能，因此我们修改.gitmodules文件，这是一个隐藏文件，打开PX4-Autopilot文件夹，单击CTRL+H，就可以显示隐藏文件，讲隐藏文件里面的github.com全部修改成github.com.cnpmjs.org，这样就可以换成国内的镜像，如下所示：

[submodule "mavlink/include/mavlink/v2.0"]
	path = mavlink/include/mavlink/v2.0
	url = https://github.com.cnpmjs.org/mavlink/c_library_v2.git
	branch = master
[submodule "src/modules/uavcan/libuavcan"]
	path = src/modules/uavcan/libuavcan
	url = https://github.com.cnpmjs.org/UAVCAN/libuavcan.git
	branch = master
[submodule "msg/tools/genmsg"]
	path = msg/tools/genmsg
	url = https://github.com.cnpmjs.org/ros/genmsg.git
	branch = indigo-devel
[submodule "msg/tools/gencpp"]
	path = msg/tools/gencpp
	url = https://github.com.cnpmjs.org/ros/gencpp.git
	branch = indigo-devel
[submodule "Tools/jMAVSim"]
	path = Tools/jMAVSim
	url = https://github.com.cnpmjs.org/PX4/jMAVSim.git
	branch = master
[submodule "Tools/sitl_gazebo"]
	path = Tools/sitl_gazebo
	url = https://github.com.cnpmjs.org/PX4/sitl_gazebo.git
	branch = master
[submodule "src/lib/matrix"]
	path = src/lib/matrix
	url = https://github.com.cnpmjs.org/PX4/Matrix.git
	branch = master
[submodule "src/lib/DriverFramework"]
	path = src/lib/DriverFramework
	url = https://github.com.cnpmjs.org/PX4/DriverFramework.git
	branch = master
[submodule "src/lib/ecl"]
	path = src/lib/ecl
	url = https://github.com.cnpmjs.org/PX4/ecl.git
	branch = master
[submodule "cmake/cmake_hexagon"]
	path = cmake/cmake_hexagon
	url = https://github.com.cnpmjs.org/ATLFlight/cmake_hexagon.git
	branch = master
[submodule "src/drivers/gps/devices"]
	path = src/drivers/gps/devices
	url = https://github.com.cnpmjs.org/PX4/GpsDrivers.git
	branch = master
[submodule "src/modules/micrortps_bridge/micro-CDR"]
	path = src/modules/micrortps_bridge/micro-CDR
	url = https://github.com.cnpmjs.org/eProsima/micro-CDR.git
	branch = master
[submodule "platforms/nuttx/NuttX/nuttx"]
	path = platforms/nuttx/NuttX/nuttx
	url = https://github.com.cnpmjs.org/PX4-NuttX/nuttx.git
	branch = px4_firmware_nuttx-7.22+
[submodule "platforms/nuttx/NuttX/apps"]
	path = platforms/nuttx/NuttX/apps
	url = https://github.com.cnpmjs.org/PX4-NuttX/apps.git
	branch = px4_firmware_nuttx-7.22+
[submodule "cmake/configs/uavcan_board_ident"]
	path = cmake/configs/uavcan_board_ident
	url = https://github.com.cnpmjs.org/PX4/uavcan_board_ident.git
	branch = master

3.更换以后，这时候会在更新子模块的时候出现一些错误，比如无法克隆等或者长时间没有进展，这个时候只需要按CTRL+Z终止下载，将下载有错误或停止的文件夹删除，之后重新下载即可。
4.下载完成以后，大概需要10分钟时间（非常快了），我们在固件的根目录打开终端，使用指令make px4fmu-v2_default(1.8版本一下，新版本的指令不是这个，具体看官网)编译。
5.此时出现错误error: expected initializer before '_PARAMS' extern double atan _PARAMS((double)); ^~~~~~~这种原因可能是因为GCC版本不对的原因，但是我们有解决办法，打开根目录，进入到src->include中，创建一个新的文件叫_ansi.h文件，里面填写如下：

/* Provide support for both ANSI and non-ANSI environments.  */

/* Some ANSI environments are "broken" in the sense that __STDC__ cannot be
   relied upon to have it's intended meaning.  Therefore we must use our own
   concoction: _HAVE_STDC.  Always use _HAVE_STDC instead of __STDC__ in newlib
   sources!
   To get a strict ANSI C environment, define macro __STRICT_ANSI__.  This will
   "comment out" the non-ANSI parts of the ANSI header files (non-ANSI header
   files aren't affected).  */

#ifndef	_ANSIDECL_H_
#define	_ANSIDECL_H_

#include <newlib.h>
#include <sys/config.h>

/* First try to figure out whether we really are in an ANSI C environment.  */
/* FIXME: This probably needs some work.  Perhaps sys/config.h can be
   prevailed upon to give us a clue.  */

#ifdef __STDC__
#define _HAVE_STDC
#endif

#ifdef _HAVE_STDC
#define	_PTR		void *
#define	_AND		,
#define	_NOARGS		void
#define	_CONST		const
#define	_VOLATILE	volatile
#define	_SIGNED		signed
#define	_DOTS		, ...
#define _VOID void
#ifdef __CYGWIN__
#define	_EXFUN(name, proto)		__cdecl name proto
#define	_EXPARM(name, proto)		(* __cdecl name) proto
#else
#define	_EXFUN(name, proto)		name proto
#define _EXPARM(name, proto)		(* name) proto
#endif
#define	_DEFUN(name, arglist, args)	name(args)
#define	_DEFUN_VOID(name)		name(_NOARGS)
#define _CAST_VOID (void)
#ifndef _LONG_DOUBLE
#define _LONG_DOUBLE long double
#endif
#ifndef _PARAMS
#define _PARAMS(paramlist)		paramlist
#endif
#else	
#define	_PTR		char *
#define	_AND		;
#define	_NOARGS
#define	_CONST
#define	_VOLATILE
#define	_SIGNED
#define	_DOTS
#define _VOID void
#define	_EXFUN(name, proto)		name()
#define	_DEFUN(name, arglist, args)	name arglist args;
#define	_DEFUN_VOID(name)		name()
#define _CAST_VOID
#define _LONG_DOUBLE double
#ifndef _PARAMS
#define _PARAMS(paramlist)		()
#endif
#endif

/* Support gcc's __attribute__ facility.  */

#ifdef __GNUC__
#define _ATTRIBUTE(attrs) __attribute__ (attrs)
#else
#define _ATTRIBUTE(attrs)
#endif

/*  ISO C++.  */

#ifdef __cplusplus
#if !(defined(_BEGIN_STD_C) && defined(_END_STD_C))
#ifdef _HAVE_STD_CXX
#define _BEGIN_STD_C namespace std { extern "C" {
#define _END_STD_C  } }
#else
#define _BEGIN_STD_C extern "C" {
#define _END_STD_C  }
#endif
#endif
#else
#define _BEGIN_STD_C
#define _END_STD_C
#endif

#endif /* _ANSIDECL_H_ */

即可。
6.继续编译，此时又会碰到一个错误converting a packed 'flash_entry_header_t' {aka 'struct flash_entry_header_t'} pointer (alignment 1) to a 'uint32_t' {aka 'unsigned int'} pointer (alignment 4) may result in an unaligned pointer value [-Werror=address-of-packed-member]，我们同样有解决办法，打开根目录，进入到cmake->common,打开px4_base.cmake，搜索werror,找到他，把他所在行删除即可，如下图所示：

7.之后就可以编译成功！（其余的一些小错误都可以直接搜到哦，下载之前一定记得系统快照以防万一！！！）